This section provides background information which is not necessarily prior art to the inventive concepts associated with the present disclosure.
Lift gates provide a convenient access to the cargo areas of hatchbacks, wagons, and other utility vehicles. Typically, the lift gate is hand operated, requiring manual effort to move the lift gate between the open and the closed positions. Depending on the size and weight of the lift gate, this effort can be difficult for some users. Additionally, manually opening or closing a lift gate can b e inconvenient, particularly when the user's hands are full.
Attempts have been made to reduce the effort and inconvenience of opening or closing a lift gate. One solution is to pivotally mount gas struts to both the vehicle body and the lift gate, reducing the force required for opening the lift gate. However, the gas struts also hinder efforts to close the lift gate, as the struts re-pressurize upon closing, increasing the effort required. Additionally, the efficacy of the gas struts vary according to the ambient temperature. Furthermore, the use of gas struts still requires that the lift gate is manually opened and closed.
U.S. Pat. No. 6,516,567 to Stone et al. (hereafter referred to as the '567 patent) provides a power actuator that works in tandem with a gas strut. The '567 power actuator comprises a motor mounted within the vehicle body coupled to a flexible rotary cable by a clutch. The flexible rotary cable drives an extensible strut that is pivotally mounted to both the vehicle body and the lift gate. Thus, the motor can raise or lower the lift gate conveniently without manual effort. A controller to engage and disengage the motor can be connected to a remote key fob button or a button in the passenger compartment, providing additional convenience. However, the power actuator described in the '567 patent is not without its disadvantages. The power actuator is comprised of multiple parts, each of which needs to be assembled and mounted to the vehicle separately, increasing costs. The vehicle body must be specifically designed to provide a space to house the motor. Due to the limited space available, the motor is small and requires the assistance of the gas strut. Additionally, because the power actuator described in the '567 patent is designed to work in tandem with a gas strut, the gas strut can still vary in efficacy due to temperature. Thus, the motor provided must be balanced to provide the correct amount of power with varying degrees of mechanical assistance from the gas strut.
U.S. Publication No. US2004/0084265 to Muller (hereinafter referred to as the '265 publication) provides various examples of power actuators working in tandem with gas struts and several alternative examples of electromechanical power actuators. These electromechanical power actuators include an electric motor coupled via a flexible rotary cable to a gearset which, in turn, is coupled via a slip clutch to a rotatable piston rod. Rotation of the piston rod causes a spindle drive mechanism to translate an extensible strut that is adapted to be pivotally mounted to one of the vehicle body and the lift gate. The slip clutch functions to permit the piston rod to rotate relative to the gearset when a torque exceeding its preload is exerted on the lift gate so as to accommodate manual operation of the lift gate without damaging the electromechanical power actuator. More specifically, the slip clutch releasably couples the gearset to the piston rod whereby, during normal operation, powered opening and closing of the lift gate is provided. However, when a high level force is applied to the extensible strut which attempts to back drive the spindle drive mechanism in response to excessive or abusive manual operation of the lift gate, the slip clutch momentarily releases the drive connection between the piston rod and the gearset to avoid mechanical damage to the system. The '265 publication also illustrates use of a helical compression spring to provide a counter balancing force against the weight of the lift gate.
U.S. Publication No. US2012/0000304 to Hamming et al (hereinafter the '304 publication) discloses several embodiments of power drive mechanisms for moving trunk lids and lift gates between open and closed positions. The power drive mechanisms have an offset configuration employing an electric motor-driven worm gearset to rotate an externally-threaded jackscrew for translating an extensible strut. A slip clutch is shown to be disposed between an output gear of the worm gearset and the rotatable jackscrew. In addition, a coupler unit is provided between the motor output shaft and the worm of the worm gearset. The coupler unit includes a first coupler member fixed for rotation with the worm shaft, a second coupler member fixed for rotation with the motor output shaft, and a resilient spider interdigitated, between fingers extending from the first and second coupler members. The resilient coupler provides axial and circumferential isolation between the first and second coupler members and functions to absorb transient or torsional shock loads between the motor shaft and the worm shaft.
U.S. Publication No. US2008/0060273 to Bochen et. al (hereinafter the '273 publication) discloses a collinear or strut-type drive device configured to house the electric motor, the slip clutch and the rotary threaded spindle unit in a common housing from which an extensible strut is guided in a telescopic manner. The slip clutch permits limited axial movement between a pair of frictionally engaged clutch members to permit relative rotation between the motor shaft and the threaded spindle shaft when required to accommodate overload conditions.
In view of the above, it is evident that electromechanical drive mechanisms of the type used in trunk lid and lift gate powered closure systems are commonly equipped with a slip clutch to accommodate manual operation as well as a resilient coupler unit to accommodate misalignment and shock loads. However, these devices can increase the cost and complexity of powered actuators as well as impact the available packaging requirements.
It is therefore desired to provide a means for raising and lowering a vehicle trunk lid or lift gate that obviates or mitigates at least one of the above-identified disadvantages of the prior art.